Project Summary Multimorbidity among older adults is prevalent, disabling, and costly. Vulnerable adults may be at even greater risk of multimorbidity earlier in the lifespan and may also experience sequelae and additional diagnoses that increase multimorbidity burden over time. Greater understanding of how disease patterns change over time and putative interactions with individual and community-level factors motivates the current proposed project that centers on the health of vulnerable adults. This work will advance the field of multimorbidity and aging in important ways by addressing key gaps in knowledge: (1) What kinds of multimorbidity patterns are most common among patients seeking care in community health centers (CHCs) and how do these patterns change over time? (2) Do community-level factors moderate the association between multimorbidity and poor health outcomes for CHC patients? (3) Do middle-aged and older adults seeking care in CHC settings demonstrate more rapid age-related declines (e.g., greater burden of multimorbidity, complex patterns of multimorbidity) compared to their non-CHC health care seeking peers? And, (4) How do health care needs and utilization change for middle-aged and older adults with multimorbidity? Our proposed research leverages clinical electronic health record (EHR) data from large networks of CHCs and non-CHCs. We anticipate important insights from findings that will inform clinical processes (workflow, clinical care decision-making) and policies that serve safety-net populations by identifying multimorbidity patterns predictive of rapid health downturns. We propose three aims to: Aim 1. Identify the prevalence, patterns, and health outcomes associated with specific multimorbidity combinations for middle-aged and older CHC patients over time and by sociodemographic factors. Aim 2. Identify community-level social determinants of health that moderate the relationship between multimorbidity combinations and disease progression, exacerbations, and mortality among middle-aged and older CHC patients. Aim 3. Specify multimorbidity prevalence and patterns over time among middle-aged and older adults seeking care in CHC relative to matched counterparts seeking care in non-CHC settings.